1. Field of the Invention
The present invention relates to a sweetener composition and to a process for the production of the sweetener composition containing the sweetening substances aspartame (APM) and N-[N-(3,3-dimethylbutyl)-L-xcex1-aspartyl]-L-phenylalanine methyl ester.
2. Discussion of Background Art
Awareness of fatness, caused by excessive sugar intake and diseases accompanied by fatness, has increased as eating habits have improved in recent years. Accordingly, there has been a need for the development of a low-calory sweetening agent (sweetener) that replaces sugar. Aspartame (APM) is widely used as a sweetening agent because of its excellent safety and quality of sweetness. However, aspartame is not very stable.
French Patent No. 2697844 discloses a derivative in which an alkyl group is introduced into an amino group of aspartic acid. It was shown that N-[N-(3,3-dimethylbutyl)-L-xcex1-aspartyl]-L-phenylalanine methyl ester, which hereinafter is abbreviated to xe2x80x9cN-(3,3-dimethylbutyl)-APMxe2x80x9d, or simply referred to as xe2x80x9cAPM derivativexe2x80x9d, exhibits improved stability and a markedly improved sweetening potency. Processes for the production of N-(3,3-dimethyl-butyl)-APM are known. For example, FR 2697844 describes a process for the reductive alkylation of APM in the presence of 3,3-dimethylbutylaldehyde and sodium cyanoborohydride in methanol. In WO95/30689, APM is reductively alkylated in the presence of 3,3-dimethylbutylaldehyde and platinum carbon as the catalyst in a mixed solvent of water and methanol at a pH of 4.5 to 5. However, when the reaction is carried out according to the processes described in the above patents, 3,3-dimethylbutylaldehyde does not react completely with APM and a byproduct, N-[N,N-di-(3,3-dimethylbutyl)-L-xcex1-aspartyl]-L-phenylalanine methyl ester having two alkyl groups, is produced.
The sweetening potencies of N-(3,3-dimethylbutyl)-APM and aspartame (APM) are reported to be 10,000 times (Japanese Patent Kohyou Publication JP-A-8-503206) and about 200 times (Japanese Patent Kokoku Publication JP-B-47-31031) that of sucrose, respectively.
The quality of sweetness of N-(3,3-dimethylbutyl)-APM is not reported in detail, however, it is extremely weak in early taste and extremely strong in later taste. Early taste and late taste are determined in comparison to sucrose. For example, a sweetener, when put in the mouth, can taste sweet as early as sucrose or later than sucrose. N-(3,3-dimethylbutyl)-APM is strong in astringency (astringent taste) and badly balanced for quality of sweetness compared to sucrose. APM is weak in early taste and strong in later taste, although improved compared to N-(3,3-dimethylbutyl)-APM. Both compounds have a quality of sweetness which is weak in early taste and strong in later taste based on sucrose.
There have been various proposals for the improvement of particularly the later taste (see, e.g., Japanese Patent Kokai Publication JP-A-56-148255, JP-A-58-141760, JP-A-58-220668, etc.). Furthermore, among the proposals are methods for obtaining a natural quality of sweetness closer to that of sucrose, for example, by the combination with sucrose (Japanese Patent Kokai Publication JP-A-57-152862).
According to the findings of the inventors, it is possible to intensify early taste, weaken later taste and to weaken the astringent taste, thereby balancing the quality of sweetness by combining N-(3,3-dimethylbutyl)-APM and APM homogeneously. A homogeneous composition of N-(3,3-dimethylbutyl)-APM and APM is improved in early taste and expected to give a high degree of sweetness as well as a balanced quality of sweetness closer to that of sucrose, compared to its singly used ingredients N-(3,3-dimethylbutyl)-APM or APM.
It is somewhat difficult to adjust the degree of sweetness when using N-(3,3-dimethylbutyl)-APM because its sweetening potency is 10,000 times (Japanese Patent Kohyou Publication JP-A-8-503206) that of sucrose. Accordingly, a combination of N-(3,3-dimethylbutyl)-APM with APM not only improves the quality of sweetness, but is also allows easy adjustment of the degree of sweetness.
It is an object of the present invention to provide a process for producing a homogeneous sweetener composition containing APM and N-(3,3-dimethylbutyl)-APM in high yields and with a high purity. An improved quality of sweetness compared to mixtures of crystals of APM and crystals of APM derivative is desired. It is another object of the present invention to provide a sweetener composition obtained by the process according to the invention.
These and other objects are achieved according to the invention, the first embodiment of which includes a process for production of a sweetener composition, comprising:
reductively alkylating aspartame and 3,3-dimethylbutylaldehyde in an amount of 3,3-dimethylbutylaldehyde at most equimolar to the aspartame in the presence of a reducing agent in a reaction solution to form a sweetener composition; separating said reducing agent from said reaction solution; crystallizing said sweetener composition and isolating a precipitated sweetener composition.
Another embodiment of the invention includes the sweetener composition produced by the above process and comprising aspartame and N-[N-(3,3-dimethylbutyl)-L-xcex1-aspartyl]L-phenylalanine methyl ester.
Another embodiment of the invention includes the sweetener composition comprising a homogeneous composition of aspartame and N-[N-(3,3-dimethylbutyl)-L-xcex1-aspartyl]-L-phenylalanine methyl ester, wherein said sweetener composition does not contain N-[N,N-di(3,3-dimethylbutyl)-L-xcex1-aspartyl]-L-phenylalanine methyl ester.
The present inventors have found that N-[N-(3,3-dimethylbutyl)-L-xcex1-aspartyl]-L-phenylalanine methyl ester (N-(3,3-dimethylbutyl)-APM)) can be produced by reductive alkylation using, for example, 1 mol of APM and an at most equimolar amount of the 3,3-dimethylbutylaldehyde to APM, i.e. 1 mole or less of 3,3-dimethylbutylaldehyde. The amount of 3,3-dimethylbutylaldehyde is preferably about 0.0003-0.28 mol, and more preferably about 0.0005-0.25 mol for 1 mol of APM. The amount of 3,3-dimethylbutylaldehyde includes all values therebetween, especially including 0.0003, 0.0004, 0.0008, 0.001, 0.002, 0.005, 0.007, 0.009, 0.011, 0.02, 0.05, 0.07, 0.09, 0.11, 0.13, 0.15, 0.17, 0.19, 0.21, 0.23, 0.25, 0.27 and 0.28 mol for 1 mol of APM.
After completion of the alkylation reaction, the reducing agent is separated from the reaction mixture. Crystallization is affected and followed by the separation of the precipitated crystals. An excellent sweetener composition containing aspartame (APM) and N-[N-(-3,3dimethylbutyl)-L-xcex1-aspartyl]-L-phenylalanine methyl ester and having a balance in quality of sweetness can be easily and efficiently produced in high yields and with high purity without producing N-[N,N-di(3,3-dimethylbutyl)-L-xcex1-aspartyl]-L-phenylalanine methyl ester as a by-product. The obtained sweetener composition is superior to those produced by simply mixing crystals of APM and crystals of the APM derivative.
A sweetener composition containing APM and the APM derivative obtained by the process according to the present invention, may be preferable as a sweetener. More preferably, the dried form is used as a sweetener. The sweetener can contain a carrier, if required. A suitable carrier can be produced or selected through the known methods for production or selection of carriers. The sweetening composition can be used as a sweetener or as a sweetening agent. Various products can be sweetened with the composition of the present invention, for example, food, cosmetics (dental rinse, mouth wash, etc.) and oral pharmaceuticals. APM and the APM derivative can be contained in the sweetener composition in a weight ratio of 0.05-50, preferable 1-40, more preferably 5-30 of the APM derivative per 100 of the APM. The weight ratio includes all values therebetween, especially including 0.05, 0.1, 0.5, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50.
Preferred, catalysts for the reductive alkylation are platinum-carbon, palladium-carbon, platinum black, palladium black, etc. (WO95/30689). However, the catalyst is not limited to these species. After completion of the reductive alkylation, the catalyst is separated from the solution containing APM and the APM derivative. The remaining solution is concentrated, if required. The crystals precipitate and are separated, yielding a sweetener composition containing homogeneous APM and the APM derivative.
Preferred solvents are water, ethyl acetate, methyl acetate, acetic acid, toluene, hexane, tetrahydrofuran, acetonitrile, dimethoxyethane, ethyl ether, isopropyl alcohol, ethyl alcohol, methyl alcohol, dichloromethane, chloroform and 1,2-dichloroethane, or mixtures thereof.
Concentration of the reaction solution before crystallization may be required to increase the yield. Therefore, it is preferable to employ an alcohol based solvent or a mixed solvent during the reaction. Preferably, water or a mixture of water and alcohol based solvent(s) is employed. The alcohol based solvent or the mixed solvent is replaced by water to allow to easily minimize the solvent in the final product. The replacement is achieved by adding a suitable amount of water to the reaction solution, and then concentrating the same.
The desired amount of APM in the composition is obtained by adjusting, for example, the amount of 3,3-dimethylbutylaldehyde, the reaction temperature or the reaction time. In addition, the weight ratio can be controlled by adding APM in an amount that exceeds the limit of its solubility before starting the reaction, and then dissolving the excess APM, for example, by heating before the separation of the catalyst. Furthermore, control of the weight ratio is possible by adding a suitable amount of APM to the reaction solution after the separation of the catalyst and dissolving the added APM. Furthermore, APM can be dissolved in the reaction solvent before starting the reaction. Alternatively, a slurry of APM may be empoloyed.
Crystallization of the composition from the reaction solution may be initiated by, for example, cooling, concentrating, or neutralizing. It is known that refined crystals may be formed under stirring. If an excess of APM has been used, the solution may be subjected to crystallization under standing (static crystallization) or to crystallization under stirring or a combination of these procedures (Japanese Patent Kokoku Publication JP-B-03-025438).
The sweetener composition can be obtained by separating the liquid and the solid material of the obtained slurry (sherbet). The solid material is then dried and granulated (pelletized), if required. Preferably, the solid material is separated from the liquid by filtration or centrifugation. The solid material may be washed after the separation. Preferably, drying can proceed by using a vacuum dryer, a fluidized-bed dryer, a spray dryer, or a micron dryer. Preferably, the granulation is achieved by dry granulating or wet granulating. However, there is no limitation to these exemplified methods.
It is an advantage of the process of the present invention to give a homogeneous composition of APM and the APM derivative. Such homogeneity is difficult to achieve when mixing separately produced APM and APM derivative crystals. The homogeneous composition does not contain N-[N,N-di(3,3-dimethylbutyl)-L-xcex1-aspartyl]-L-phenylalanine methyl ester. Preferably, it contains N-[N,N-di(3,3-dimethylbutyl)-L-xcex1-aspartyl]-L-phenylalanine methyl ester in an amount of less than 5%, more preferably less than 2.5%, even more preferably less than 1% and most preferably less than 0.5%.
Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only, and are not intended to be limiting unless otherwise specified.